1. Field of the Invention
The present invention relates to a propeller shaft assembly of a vehicle.
2. Description of the Related Art
Conventional propeller shafts include those of the type that absorbs impact loads caused by, for example, a vehicle crash, as disclosed in publications such as Japanese Patent Application Laid-Open No. 11-303846 (Reference Document 1) and No. 7-305715 (Reference Document 2).
The propeller shaft described in Reference Document 1 has an outer shaft spline-engaged with inner shafts. The end of each of the inner shafts is caulked at an extended portion of the outer shaft. When excessively high impact loads caused by crushing or the like are exerted, the caulked portion is plastically deformed, and the end of the inner shaft comes off from the caulked portion. The inner shafts and the outer shafts retract, and the impact load is consequently absorbed and relaxed.
The propeller shaft described in Reference Document 2 has an outer shaft spline-engaged with inner shafts. A taper portion formed in a free end portion of each inner shaft is axially engaged with a taper portion around an inner periphery of the outer shaft. When excessively high impact loads caused by crushing or the like are exerted, the axial engagement in the taper portion is released. The inner shafts and the outer shaft retract, and the impact loads are absorbed and relaxed.
In the propeller shaft assembly described in Reference Document 1, while the inner shaft is prevented from being disengaged from the outer shaft, a snap ring for determining a projection position of the inner shaft with respect to the outer shaft is fitted into a groove provided in the end portion of the inner shaft.
As described above, the propeller shaft described in Reference Document 2 has the outer shaft spline-engaged with the inner shafts. The taper portion formed in the free end portion of the inner shaft is axially engaged with the taper portion around the inner periphery of the outer shaft. When excessive impact loads caused by crushing are exerted, the axial engagement in the taper portion is released. The inner shafts and the outer shaft retract, and the impact loads are absorbed and relaxed.
In the propeller shaft described in the Reference Document 1, a shock absorbing section is formed by caulking the end of the outer shaft. As such, processing is complex, and manufacturing costs are increased.
In addition, in the propeller shaft described in the Reference Document 1, the snap ring needs to be fitted to the end portion of the inner shaft. This results in increases in components as well as assembly steps, also leading to an increase in costs.
Further, in the propeller shaft described in Reference Document 1, the groove is provided in the end portion of the inner shaft to receive the snap ring, and the end portion of the inner shaft is caulked in the extended portion of the outer shaft. This can cause the groove to be closed or damaged with caulking loads being exerted to on the end portion of the inner shaft, consequently easing disengagement of the snap ring.
In the propeller shaft described in Reference Document 2, the axial engagement portion (taper portion) of the inner shaft with respect to the outer shaft is provided in the free end portion. Nevertheless, the axial engagement portion is integral in material with the splined portion. In this case, the influence of shakiness in the rotational direction of the spline engagement between the outer shaft and the inner shaft extends to the axial engagement portion. This consequently disables high-accuracy setting of long-term steady engagement strength of the axial engagement portion between the outer shaft and the inner shaft.
An object of the present invention is to provide a propeller shaft assembly including a shock absorbing section that is constructed simply and with high accuracy to secure stability in shock absorbing performance of the propeller shaft assembly.
In the propeller shaft assembly described in the Reference Document 1, two mutually adjacent first and second shock absorbing sections are disposed parallel to each other along the axial direction. The mutually adjacent shock absorbing sections are individually provided to two ends of the common outer shaft. The one shock absorbing section connects the one inner shaft to the outer shaft, and the other shock absorbing section connects the other inner shaft. Impact loads acting on the vehicle which are absorbed initially cause the one inner shaft to retract with respect to the outer shaft in the first shock absorbing section. The loads then cause the one inner shaft to slide into a hollow portion of the outer shaft by a first shock absorption stroke. In this manner, the loads are absorbed and relaxed. However, a case can occur in which the impact load is not fully absorbed. In this case, residual loads cause the outer shaft to retract with respect to the other inner shaft in the second shock absorbing section. The loads then cause the outer shaft to slide about the other inner shaft by a second shock absorption stroke. In this manner, the impact loads are further absorbed and relaxed.
In the propeller shaft assembly described by Reference Document 1, in the stage where the mutually adjacent first and second shock absorbing sections act in series to absorb and relax impact loads, the two inner shafts slide in series into the outer shaft by the first and second shock absorption strokes. However, since the two inner shafts are disposed along the same axis, the outer shaft needs to have a marginal length to be longer than the total length of the first and second shock absorption stroke. Consequently, the overall length of the propeller assembly shaft needs to be increased, accordingly leading to an excessive increase in the weight of the shaft.
To solve this problem, another object of the invention is to secure predetermined shock absorption strokes without increasing the overall length of the propeller shaft assembly in which a plurality of shock absorbing sections are disposed.